1. Field of the Invention
This invention relates to a toner used in image-forming processes such as electrophotography, electrostatic recording, electrostatic printing and toner jet recording, and also relates to an image-forming method and a process cartridge which make use of the toner.
2. Related Background Art
A number of methods as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 and No. 43-24748 are known as methods for electrophotography. In general, recorded images are obtained by forming an electrostatic latent image on a photosensitive member by various means utilizing a photoconductive material, subsequently developing the latent image by the use of a toner to form a toner image, and transferring the toner image to a transfer medium such as paper as occasion calls, followed by fixing by the action of heat, pressure, heat-and-pressure, or solvent vapor.
In recent years, as copying machines and printers have been made to have multiple function, to record images in a higher image quality and to have a higher process speed, toners have also become required to have much severer performances. Accordingly, toners are made smaller in particle diameter and are required to have particle size distribution which is sharp enough to contain no coarse particles and less ultrafine powder.
Making toners have a smaller particle diameter can improve the resolution and sharpness of images, but brings about various problems.
For one thing, making a toner have a small particle diameter results in a large specific surface area of the toner and hence a broad distribution of its charge quantity, to tend to cause fog on non-image areas when the toner participates in development. Also, the chargeability of toners more tends to be affected by environment. In order to make this fog less occur, it is also attempted to make toners have a sharp particle size distribution. This, however, may be the cause of a cost increase due to, e.g., a low yield in the production of toners.
Moreover, where toners are made to have a small particle diameter, the dispersibility of other internal additives in binder resin tends to more affect the performances of toners.
To cope with such problems, it is common to add charge control agents to toners in order to impart the desired triboelectric charges to the toners.
Nowadays, charge control agents known in the present technical field include, metal complexes of monoazo dyes, metal complexes of hydroxycarboxylic acids, dicarboxylic acids or aromatic diols and resins containing acid components, which are known as negative triboelectric charge control agents. As positive triboelectric charge control agents, Nigrosine dyes, azine dyes, triphenylmethane dyes, quaternary ammonium salts and polymers having a quaternary ammonium salt in the side chain are known in the art. Most of these charge control agents, however, are color agents and are often not usable in color toners.
In addition, some charge control agents have disadvantages that it is difficult to balance image density and fog, it is difficult to attain sufficient image density in a high-humidity environment, they have a poor dispersibility in resins, and they may adversely affect storage stability, fixing performance and anti-offset properties.
In recent years, from the viewpoint of triboelectric charge control and safety, studies are being made on charge control resins. Japanese Patent Application Laid-Open No. 63-184762 discloses a method in which a polymer of a styrene monomer with 2-acrylamido-2-methylsulfonic acid is used. Japanese Patent Application Laid-Open No. 3-161761 discloses a method in which the polymer of a styrene monomer with 2-acrylamido-2-methylsulfonic acid is used as a charge control agent with respect to a polyester resin. Japanese Patent Application Laid-Open No. 2000-56518 discloses a toner which contains as a charge control agent a sulfonic-acid-group-containing acryl- or methacrylamide copolymer having a specific glass transition temperature. These methods can provide a superior triboelectric chargeability, but can not be said to be satisfactory in respect of any environmental variation, lapse of time and condition of use which are to be dealt with adequately as the toners are made to have a smaller particle diameter, in particular, on making image quality higher, and also in respect of an improvement in transfer efficiency taking account of environmental problems as stated later.
In the above photographic process, transfer residual toner is present on the photosensitive member after the toner image has been transferred from the surface of the photosensitive member to the transfer medium. In order to perform continuous copying quickly, this residual toner on the photosensitive member must be removed by cleaning. The residual toner thus removed and collected is further put into a container or collection box provided inside the main body, and thereafter discarded or recycled through a circulation step.
To grapple with environmental problems, a construction designed to provide a recycle system inside the main body is required as a waste-tonerless system. However, in order to make copying machines and printers have multiple function, record images in a higher image quality and have a higher process speed, a fairly large recycle system is required in the main body, resulting in large copying machines and printers in themselves. This is not feasible for making machines small-size from the viewpoint of space saving. The same applies also in a system in which the waste toner is held in a container or collection box provided inside the main body and a system in which the photosensitive member and the part where the waste toner is collected are set in one unit.
To deal with these adequately, it is necessary to improve the transfer efficiency required when the toner image is transferred from the surface of the photosensitive member to the transfer medium.
Japanese Patent Application Laid-Open No. 9-26672 discloses a method in which in a toner produced by pulverization a transfer efficiency improver having an average particle diameter of 0.1 to 3 xcexcm and a hydrophobic fine silica powder having a BET specific surface area of 50 to 300 m2/g are incorporated so that the toner can have a low volume resistance and the transfer efficiency improver can form a thin-film layer on the photosensitive member so as to improve the transfer efficiency. However, since the toner produced by pulverization has particle size distribution, it is difficult to afford a uniform effect on all particles. Accordingly, it is necessary to make further improvement.
As a means for improving the transfer efficiency, Japanese Patent Application Laid-Open No. 3-84558, No. 3-229268, No. 4-1766 and No. 4-102862 disclose toners produced by processes such as spray granulation, solution dissolution, and polymerization so that toner particles can have a shape close to spheres. Production of such toners, however, not only requires large-scale equipment, but also tends to cause a problem concerned with cleaning just because of the toner particles made close to true spheres.
As common processes for producing toners, a binder resin for making toner fix to transfer mediums, a colorant of various types for giving color to toner and a charge control agent for imparting electric charges to toner particles are used as materials. In addition to such materials, in one-component development as disclosed in Japanese Patent Application Laid-Open No. 54-42141 and No. 55-18656, a magnetic material of various types for imparting transport performance to the toner itself is added. If necessary, other additives such as a release agent and a fluidity-providing agent are further added, and these are dry-process mixed. Thereafter, the mixture obtained is melt-kneaded by means of a general-purpose kneading machine such as a roll mill or an extruder, followed by cooling to solidify, and then the kneaded product is crushed. The crushed product obtained is pulverized by means of a grinding machine of various types such as a jet-stream grinding machine and a mechanical-impact grinding machine. Then the pulverized product obtained is introduced into an air classifier of various types to carry out classification to obtain toner particles put to have particle diameters necessary as toners, optionally followed by further external addition of a fluidizer or a lubricant and dry-process blending to obtain toners. Also, in the case of two-component developers, the above toners are used after they are blended with various carriers.
In order to obtain fine toner particles as stated above, a conventional process shown in FIG. 10 as a flow chart is commonly employed.
The crushed product for toner is continuously or successively fed into a first classification means. Classified coarse powder composed chiefly of a group of coarse particles larger than a prescribed particle size is pulverized by means of a pulverization means, and thereafter circulated to the first classification means again.
Other finely pulverized product for toner which is composed chiefly of particles within the prescribed particle size and particles smaller than the prescribed particle size is sent to a second classification means, and is classified into median powder composed chiefly of a group of particles having the prescribed particle size and fine powder composed chiefly of a group of particles smaller than the prescribed particle size. However, where toners are made to have smaller particle diameter, electrostatic agglomeration between particles may greatly occur. The toner particles which are originally to be sent to the second classification means are circulated to the first classification again to tend to produce excessively pulverized fine powder and ultrafine powder.
Various types of grinding machines are used as pulverization means. To pulverize the crushed product composed chiefly of binder resin, a jet-stream grinding machine, in particular, a collision air grinding machine making use of jet streams as shown in FIG. 13 is used.
In the collision air grinding machine making use of high-pressure gas such as jet streams, a powder material is transported by jet streams and jetted from an outlet of an accelerating tube to cause the powder material to collide against the colliding surface of a collision member provided facing the open end of the outlet of the accelerating tube, and the powder material is pulverized by the aid of impact force of the collision.
In the collision air grinding machine shown in FIG. 13, a collision member 164 is provided facing an outlet 163 of an accelerating tube 162 to which a high-pressure gas feed nozzle 161 is connected. By the aid of high-pressure gas fed to the accelerating tube 162, the powder material is sucked into the accelerating tube 162 from a powder material feed opening 165 made to communicate with the accelerating tube 162 at its halfway point. The powder material is jetted together with the high-pressure gas, caused to collide against a colliding surface 166 of the collision member 164, and pulverized by the aid of the impact force of the collision. The pulverized product is discharged out of a pulverization chamber 168 through a pulverized product discharge opening 167.
However, since the above collision air grinding machine is so constructed that the powder material is jetted together with the high-pressure gas, caused to collide against the colliding surface of the collision member, and pulverized by the aid of impact force of the collision, the toner particles thus obtained by pulverization may be amorphous and have a squared shape.
Japanese Patent Application Laid-Open No. 2-87157 discloses a method in which toner particles produced by pulverization are subjected to mechanical impact (hybridizer) to modify the shape and surface properties of the particles so as to improve transfer efficiency. This method, however, requires to further provide a post-treatment step for the pulverization, and hence it can not be said to be a preferable method in view of the productivity of toners and also because the toner particle surfaces become close to an unevenness-free state to necessitate an improvement with respect to development.
With regard to the classification means, various types of gas current classifiers and methods are proposed. Among them, a classifier making use of a rotating blade and a classifier having no movable part are available. Of these, the classifier having no movable part includes a stationary wall centrifugal classifier and an inertial classifier. Such a classifier that utilizes an inertia force is disclosed in Japanese Patent Publication No. 54-24745 and No. 55-6433 and Japanese Patent Application Laid-Open No. 63-101858.
In these gas current classifiers, as shown in FIG. 8, a powder material is jetted into a classification zone of a classifying chamber together with gas currents at a high speed from a feed nozzle having an opening at the classification zone. In the classifying chamber, a centrifugal force of curved gas currents flowing along a Coanda block 145 separates the powder material into coarse powder, median powder and fine powder, and edges 146 and 147, having slender tips, classify it into the coarse powder, the median powder and the fine powder.
In such a conventional classifier 57, a finely pulverized material is introduced from a material feed nozzle. Powder particles flowing inside pyramidal tubes 148 and 149 have a tendency of flowing with a screwing force acting straight in parallel to the tube walls. In the material feed nozzle, however, the powder material separates roughly into an upper stream and a lower stream when introduced from the upper part. Light fine powder tends to be contained in the upper stream in a large quantity, and heavy coarse powder in the lower stream in a large quantity, where the corresponding particles flow independently. Hence, depending on the portion from which the powder material is introduced into the classifier, the respective flows may draw different loci or the coarse powder disturbs the locus of the fine powder, bringing about a limitation to the improvement in classification precision and also tending to lower the precision when a powder material containing coarse particles of 20 xcexcm or larger diameter in a large quantity is classified.
In general, toners are required to have many and different properties. To attain such required properties depends on base materials to be used of course, and also on production methods in many cases. In the classification step for toners, classified particles are required to have a sharp particle size distribution. It is also sought to produce good-quality toners at a low cost, in a good efficiency and stably.
In addition, in order to improve image quality in copying machines and printers, toners are made smaller in particle diameter and are required to have particle size distribution which is sharp enough to contain no coarse particles and less ultrafine powder. In general, as substance becomes finer, interparticle force acts more greatly. The same applies to resins and toners, and particles become more greatly agglomerative to one another as they become finer in size.
Especially when it is attempted to obtain a toner having a weight-average particle diameter of 10 xcexcm or smaller and a sharp particle size distribution, any conventional apparatus and methods cause a lowering of classification yield. Also when it is attempted to obtain a toner having a weight-average particle diameter of 8 xcexcm or smaller and a sharp particle size distribution, any conventional apparatus and methods especially not only cause a lowering of classification yield, but also tend to result in inclusion of ultrafine powder in a large quantity.
Moreover, in the toners made to have smaller particle diameter, what is relatively important is the compatibility of individual materials contained in toners, so that a severer restriction than ever is imposed in respect of developing performance, too.
Namely, inclusive of the productivity of the toner itself, it is long-awaited to provide a toner having a high developing performance, which has been improved in transfer efficiency for the purpose of lessening the transfer residual toner on the photosensitive member, which is left as waste toner.
An object of the present invention is to provide a toner having a transfer efficiency high enough to leave less waste toner.
Another object of the present invention is to provide a toner which can maintain good developing performance even with its particle diameter made smaller.
Still another object of the present invention is to provide a toner which is not affected by any environment of image reproduction, and can maintain a good developing performance even in a high-temperature high-humidity environment and in a normal-temperature low-humidity environment.
A further object of the present invention is to provide a toner which can be produced in a high productivity with ease by pulverization.
A still further object of the present invention is to provide an image-forming method which make use of the above toner.
A still further object of the present invention is to provide a process cartridge which has the above toner.
To achieve the above objects, the present invention provides a toner comprising toner particles containing at least (i) a binder resin, (ii) a colorant and (iii) a sulfur-containing compound selected from the group consisting of a sulfur-containing polymer and a sulfur-containing copolymer, wherein;
the toner has a weight-average particle diameter of from 5 xcexcm to 12 xcexcm; and
the toner has, in its particles of 3 xcexcm or larger in diameter, at least 90% by number of particles with a circularity a of 0.900 or higher as determined from the following expression (1):
Circularity a=L0/Lxe2x80x83xe2x80x83(1)
where L0 represents the circumferential length of a circle having the same projected area as a particle image, and L represents the circumferential length of the particle image;
and in which;
a) the relationship between cut rate Z and toner weight-average particle diameter X satisfies the following expression (2):
Cut rate Zxe2x89xa65.3xc3x97Xxe2x80x83xe2x80x83(2)
provided that the cut rate Z is represented by the following expression (3):
Z=(1xe2x88x92B/A)xc3x97100xe2x80x83xe2x80x83(3)
where A is the particle concentration of the whole measured particles as measured with a flow-type particle image analyzer FPIA-1000, manufactured by Toa Iyou Denshi K.K., and B is the particle concentration of measured particles of 3 xcexcm or larger in circle-corresponding diameter; and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (4):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.51xc3x97Xxe2x88x920.645xe2x80x83xe2x80x83(4)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm; or
b) the relationship between the cut rate Z and the toner weight-average particle diameter X satisfies the following expression (5):
xe2x80x83Cut rate Z greater than 5.3xc3x97Xxe2x80x83xe2x80x83(5);
xe2x80x83and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (6):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.37xc3x97Xxe2x88x920.545xe2x80x83xe2x80x83(6)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm.
The present invention also provides an image-forming method comprising the steps of:
forming an electrostatic latent image on an electrostatic-image-bearing member;
developing the electrostatic latent image with a toner held in a developing means, to form a toner image;
transferring the toner image thus formed, to a transfer medium via, or not via, an intermediate transfer member;
fixing the toner image held on the transfer medium, to the transfer medium by heat-and-pressure fixing means; wherein;
the toner comprises toner particles containing at least (i) a binder resin, (ii) a colorant and (iii) a sulfur-containing compound selected from the group consisting of a sulfur-containing polymer and a sulfur-containing copolymer, wherein;
the toner has a weight-average particle diameter of from 5 xcexcm to 12 xcexcm; and
the toner has, in its particles of 3 xcexcm or larger in diameter, at least 90% by number of particles with a circularity a of 0.900 or higher as determined from the following expression (1):
Circularity a=L0/Lxe2x80x83xe2x80x83(1)
where L0 represents the circumferential length of a circle having the same projected area as a particle image, and L represents the circumferential length of the particle image;
and in which;
a) the relationship between cut rate Z and toner weight-average particle diameter X satisfies the following expression (2):
Cut rate Zxe2x89xa65.3xc3x97Xxe2x80x83xe2x80x83(2)
provided that the cut rate Z is represented by the following expression (3):
Z=(1xe2x88x92B/A)xc3x97100xe2x80x83xe2x80x83(3)
where A is the particle concentration of the whole measured particles as measured with a flow-type particle image analyzer FPIA-1000, manufactured by Toa Iyou Denshi K.K., and B is the particle concentration of measured particles of 3 xcexcm or larger in circle-corresponding diameter; and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (4):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.51xc3x97Xxe2x88x920.645xe2x80x83xe2x80x83(4)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm; or
b) the relationship between the cut rate Z and the toner weight-average particle diameter X satisfies the following expression (5):
Cut rate Z greater than 5.3xc3x97Xxe2x80x83xe2x80x83(5);
xe2x80x83and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (6):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.37xc3x97Xxe2x88x920.545xe2x80x83xe2x80x83(6)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm.
The present invention still also provides a process cartridge comprising an electrostatic-image-bearing member and a developing means for developing with a toner an electrostatic latent image formed on the electrostatic-image-bearing member;
the electrostatic-image-bearing member and the developing means being supported in one unit to constitute the process cartridge, and the process cartridge being detachably mountable to the main body of an image-forming apparatus; wherein;
the toner comprises toner particles containing at least (i) a binder resin, (ii) a colorant and (iii) a sulfur-containing compound selected from the group consisting of a sulfur-containing polymer and a sulfur-containing copolymer, wherein;
the toner has a weight-average particle diameter of from 5 xcexcm to 12 xcexcm; and
the toner has, in its particles of 3 xcexcm or larger in diameter, at least 90% by number of particles with a circularity a of 0.900 or higher as determined from the following expression (1):
xe2x80x83Circularity a=L0/Lxe2x80x83xe2x80x83(1)
where L0 represents the circumferential length of a circle having the same projected area as a particle image, and L represents the circumferential length of the particle image;
and in which;
a) the relationship between cut rate Z and toner weight-average particle diameter X satisfies the following expression (2):
Cut rate Zxe2x89xa65.3xc3x97Xxe2x80x83xe2x80x83(2)
provided that the cut rate Z is represented by the following expression (3):
Z=(1xe2x88x92B/A)xc3x97100xe2x80x83xe2x80x83(3)
where A is the particle concentration of the whole measured particles as measured with a flow-type particle image analyzer FPIA-1000, manufactured by Toa Iyou Denshi K.K., and B is the particle concentration of measured particles of 3 xcexcm or larger in circle-corresponding diameter; and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (4):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.51xc3x97Xxe2x88x920.645xe2x80x83xe2x80x83(4)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm; or
b) the relationship between the cut rate Z and the toner weight-average particle diameter X satisfies the following expression (5):
Cut rate Z greater than 5.3xc3x97Xxe2x80x83xe2x80x83(5);
xe2x80x83and
in the particles of 3 xcexcm or larger in diameter of the toner and in the number-based circularity distribution of the circularity a, the relationship between the number-based cumulative value Y of particles with a circularity a of 0.950 or higher and the toner weight-average particle diameter X satisfies the following expression (6):
Number-based cumulative value Y of particles with a circularity a of 0.950 or higherxe2x89xa7exp 5.37xc3x97Xxe2x88x920.545xe2x80x83xe2x80x83(6)
provided that the toner weight-average particle diameter X is from 5.0 xcexcm to 12.0 xcexcm.